For free kicks I used to mess around with all the extra controls you get for dip, swerve, etc but never used to score. Now I just get the power bar upto 1/2 way (just under if just outside the box, and obviously just over if a little further away) and just let it go. I find that I now force the keeper into a save or score 9 times out 10.
When playing against other people, its useful to have a player like Ronaldinho who is difficult to knock off the ball and use him to simply run past people (also using R2 for close control) but this is almost impossible against the CPU.
I also like to play with AC Milan, start from the keeper, pass out right to Cafu and run forwards till I meet an opposing player then pass squarely all the way across to Maldini, this gives him a lot of room and the chance to use through ball to Gilardinho, then cross the ball and hope for the best lol.